The present invention relates to an improvement in a printer, an electronic typewriter and other printing apparatus.
Generally, a printing apparatus includes two guide members which extend between a pair of side frames, and a carrier loaded with a printing mechanism and movable on and along the guide members. Specifically, while the guide members extend in parallel to a platen which is rotatably supported by the side frames, the carrier is driven by a space motor to slide on the guide members along the platen to thereby print out characters and others on a paper, which is wrapped around the platen. A prerequisite for accurate printing, therefore, is that the carrier be spaced by a constant amount from the platen and prevented from shaking up and down during its movement along the platen. To insure accurate relative position of the platen and guide members, it has been customary to fasten the guide members to the side frames by screws in parallel to the platen.
A problem with such a prior art printing apparatus is that since the fastening of the guide members to the side frame is performed during assembly of the apparatus, it has to be implemented with considerably accurate assembling work at the sacrifice of efficiency and cost.
A gear pulley which is rotated by the space motor adapted to move the carrier along the platen is rotatably supported by the output shaft of the motor through a bearing. In this kind of pulley support structure, to prevent the pulley from slipping off the motor output shaft, the bearing is press-fitted in a bore which is formed through the pulley and provided with a slightly smaller outside diameter than the bearing, whereby the pulley and the bearing are fixed to each other. Subsequently, the motor output shaft is inserted in a bore of the bearing and, then, E-rings or like stops are fitted on the shaft at opposite sides of the bearing. This allows the pulley to be rotatably supported on the motor output shaft while being prevented from slipping off the latter.
A disadvantage of the above support structure which relies on press-fitting is that the bearing which is press-fitted in the pulley increases the outside diameter and, therefore, the circumference of the pulley. The increment of the circumference of the pulley directly translates into that of the amount of drive of a member which is driven by the pulley in contact with the circumferential surface of the latter, resulting in inaccurate drive. Hence, in the case of such a gear pulley which is driven by a space motor adapted to drive a carrier along a platen, it is impossible to control the intercharacter spacing with accuracy. Specifically, a space wire is wrapped around the gear pulley and connected to the carrier, while the gear pulley is driven in a rotational motion by the space motor as stated. In this arrangement, even if the space motor is rotated stepwise to rotate the gear pulley, the amount of feed of the carrier becomes deviated from the one which was expected at the time of design of the gear pulley, due to the change in the circumference of the gear pulley.
Meanwhile, in a printer of the type using a type wheel, or daisy wheel as generally referred to, a carriage is rotatably supported by a carrier which is movable along a platen. Mounted on the carriage are a selection motor which carries a type wheel at the tip of its output shaft, a hammer solenoid for hammering the back of a type which is provided on the type wheel, etc. As the carrier is moved along the platen, the hammer solenoid hits against the back of a type on the type wheel to thereby print out information on a paper which is loaded on the platen. The carriage may be manually rotated rearward away from the platen to a predetermined position where the type wheel can be replaced with another.
In a prior art printer of the type described, however, the available range of rearward movement of the carriage is not more than about 60 degrees as measured from a predetermined print position. Hence, the space available between the type wheel in the rearward position and the platen, paper guide and others is too narrow to insert fingers for the replacement of the type wheel.
The printer using a type wheel is provided with an implementation for deciding whether a type wheel is loaded in the printer or not. This implementation consists of a reflecting or a transmitting portion provided in the type wheel itself, and a photosensor cooperative with the reflecting or transmitting portion. However, such an implementation is ineffective when it comes to type wheels which are not provided such a reflecting or a transmitting portion. Specifically, even if no type wheel is loaded in the printer, the photosensor would determine that a type wheel is present in the printer and allow the printer to operate, damaging the hammer, platen and others. For this reason, the kind of type wheels usuable with such a printer is limited to in turn limit the applicable range of a printer and other printing apparatus.
Further, the housing of a printer is usually made up of a top cover for covering a printing mechanism, a front cover for openably closing an opening which is formed through the top of the top cover, and a silencing cover attached to the front cover. The top cover is provided with various kinds of openings in addition to the top opening, e.g., an opening for mounting a platen knob, openings for receiving various kinds of operating knobs, and openings for accommodating various kinds of connectors. The top cover is customarily produced by molding resin, and a mold used is moved in the up-down direction with respect to the top cover. Hence, those openings provided in the direction of movement of the mold, i.e., provided on the top of the top cover can be formed with ease.
However, the top cover has to be provided with openings not only through its top but also through its both sides. Examples of such side openings are the opening for a platen knob and those for various connectors. Among such openings, those which open at the upper or lower end of the top cover as well may be formed as easily as those which are provided at the top, but those which are not open at the upper or lower end of the top cover have to be implemented with an extra mold, which is movable in a direction other than the up-down direction (a direction in which the openings are formed), or an extra machining step which follows a molding step. This increases the production cost of the top cover and, therefore, that of the entire printing apparatus.